Problem: What is the greatest common factor of $25$ and $15$ ? Another way to say this is: $\operatorname{gcf}(25, 15) = {?}$
The greatest common factor is the largest number that is a factor of both $25$ and $15$ The factors of $25$ are $1$ $5$ , and $25$ The factors of $15$ are $1$ $3$ $5$ , and $15$ Thus, the greatest common factor of $25$ and $15$ is $5$. $\operatorname{gcf}(25, 15) = 5$